Centrifugal fan wheel



ocf. 2s, 1956 Filed Nov. '7, 1952 D. l. DoYLE 2,767,906

CENTRIFUGAL FAN WHEEL 2 shets-sheet 1 l V l l I I I l l l I I l lJNVENTOR: DEWEY I. DOYLE BY Oct. 23, 1956 D. LDOYLE 2,767,906

-CENTRIFUGAL FAN WHEEL lFiled Nov. 7, .1952 2 Sheets-Sheet 2 FIiG. 3

' INVENTOR: DEWEY l. DOYLEv BY United aStates Patent {lice 2,767,9dhPatented Oct. 23, 1956 V2,76'7g'906 CENTRIFJUGAL Dewey I. Doyle, GrandRapidsLMich.,{assigner-itu'Doyle Vacuum 'Cleaner Compny, Grand Rapids,Mich., a 'corporation yof Michigan Application November 7, 1952.serriNo. s195`7s "8 Claims (Cl. 2304134) 'This Yinvention relates ingeneral lto centrifugal fan wheelsy andis more particularly directed to.improvements in -suc'h Vfan wheels which are especially'd'esign'e'dtocreateeither a suction or ablowing elect. I,

The improved centrifugal rfan wheel 'embed uin'g V1the upresent4invention may have Vmany uses in l'co'mbiriation with various types -ofmachines lto produce .various results.

However, the .particular design disclosed xher'e'inis especiallyadapted-for use in vacuum cleaners.

4It has been customary in the past to design 'Vacuum cleaners either forthe production `of'liigh volume `-o'r'fr the production of what'isIknown as fa'high s'taticsiiction. In lcommercial or 'industrial tanktype vaciiurn 'cleaners the particular design has in the 'past depended`upon 'the 'enduse of the vacuum cleaner. Where the purchaserf theproduct expects to'use the vacuum cleaner Awith lthe hose substantiallyopen h`e is more interested in a 'high volume of air 4passing throughthe y'maehine i However, where the machine is to be usedundefrci'rcumstances where the hose end `willvbe Vpartially 'closed`'such as in the cleaning of r-u'gsva'nd upholstered furniture, it ismore desirable that la hi'g'h static condition prevail. IUp to -thepresent ytime -vacu'm cleaner'sfwhich refdsigned to produce a high"volume inherently ihave la 'low static condition; likewise, a machinethat is especia y designed to produce la high static will inherently'result in a reduced volume. v n

In order tomore clearly 'understand 'the 'terms high orkllow static andhigh or low'ioltiinefv a brief 'description ofthe test involved indetermining 'these factors will'bepresented. The actual amount'of staticor vluriie is customarny stated in reims of wafer un. 'rn 'refiningtests to determine these faetors, a 'U-'shap'ed'tbeiis v:einployedhavinga predetermined number of inches of lwater therein. One end 'of vthe Utube 'remains 'open itty the atmosphere and lthe other end of the Uftubeis connected by means of -a hose to an opening in "the side ofthe inletinto the vacuum cleaner tank. With 'the machine 'in 'operation andcreating a vacuum at the iiile't to the tank the water lift will -beincreased as the size ffthefinlet is decreased. When the inlet iscompletely closed the number of inches ythat the 'water'is vdrawnupwardly into one side of the ll tube and is forced downwardlyin theother side of the 'U tube is l'referred to as the closed water -li-ft.This -is a measure of the vstatic suction. l

As the inlet opening to the tank is enlarged in area the water in the AUtube will fall and the number of inches of wa'ter lift for 'a given'size opening may then be'trans'lated into terms of volume.

`Industrial 'tank type vacuum cleaners designed paracularly te produce'alhign volume :or .1a relatively nigh Wafer lift :W'le'n l:the inlet Kthe 'tank fis I'clrfplfl-y fqop'n `trsmily'have a single ran wheneminoaly a s'rngflestage. Fan 'wheeiswhich haveiaa-depsig dr" thepresent time when used as asiriglesxtage are' pable of prod'cing 'averyhigh static suction and e'an therefore sensed:onlyrdrspeciae purp''ses,

.-.In order to increase the static suction ina vacuum "cleaner it'iscustomary to increase the number of ian wheelstotwo `or three andsometimes more all mounted 'bo`n`the sarnemotor shaft. These arecommonly termed lmultistage units the number of stages depending upon4tlie"'r1urritier"of'fan wheels used. When this is done it becomesnecessary .that the air pass through the center and out of -*theAperiphery of the'iirst fan wheel and-then he `"direetedbackinto'thecenter 'of the second wheel and "so don until `'the periphery ofthe last wheel is reached. The result y'of this construction is toincrease the static suction or closed water lift but, at the same time,the volurneof air passing through the machine will be materiallyreduced.

The present invention is directed 'to a novel form of centrifugal'fanwhee'l which is Vcapable of vproducing in a single wstage ymachine-a relatively Vhigh static suction 'as well'as a "relatively high volumewherebythe saine machine-may have its end uses multiplied considerably,iijer., a'machine embodying the present invention will be :usable "for'any purpose whether a 'high volume or a high static A-is desired Inview of the foregoing it is therefore Vone of the 'principal vobjects ofthe present invention to provide a 'centrifii'gal fa'n wheel which iscapable of producing a relatively high static 'suction and arelativelyhigh volume in a'single stage vacuum cleaner.

Another object of the invention is to Y'provide a centrifugal fan wheelfor use in either vacuum :producing machines or blowers which willproduce a higher static condition in a singleist'age machine "than in amultistage 'machine of the same size presently in use and which willalso produce a'hig'her volume `than the volume type machines presentlyin use. n

A further object of the invention is to provide'a centrifugal fan Awheelwhich includes apair of axially spaced disks wherein a plurality ofblades having an involute form lare kdisizvfose'd vbetween thosel disks.

A still 'further object Vof the invention is to provide fa centrifugal'fan wheel wherein two disks 'are spaced apart iin an axial directionwith a plurality yof blades located between the disks and wherein eachblade is yin the form of an involute and arranged around the wheel withthe 'center of the generating circle vfor the involute `being noffsetfrom the center of the wheel. v

Still another object of the invention is to provide a centrifugal 'fanwheel fora compressible'fluid wherein a `plurality of involute bladesare disposed between two flat disk-s. These blades are soarranged aroundthe wheel that the inletarea 1between adjacent blades at the innerorheelends thereof is ygreater than the outlet area between `adjacentvblades at 'the outer or tip ends thereof whereby the iluid passing`through the space between adjacent blades `will be compressed.

yStill further and speciic object of the invention is toprovideialcent'rifugal fan wheel adapted for use with coin- "pre'ss'iblefluids wherein a plurality of blades of involute formare 'equallylspaced around 'the wheel between two at disks and wherein the center ofthe generating circle for each involute blade is offset from the centerof the wheel approximately the radius of the generating circle. It isalso a specific object of the invention to form the involute blades'using a generating circle having a diameter approximately one-sixth theIdiameter o'f the fan wheel -forrned by `the ydisks lbetween which vtheblades are located Whereby to achieve proper length of air passage andproper' heel and tip angles to result in maximum static and'volume"conditions ina vacuum producing machine. Other 'objects and 'advantages'of the invention will be- 'eine apparent upon reading the followingdescription taken in conjunction with the accompanying drawings inwhich:

Fig. l is a perspective view of a fan wheel embodying the presentinvention;

Fig. 2 is a horizontal sectional view through the fan wheel taken alongthe plane of line 2-2 of Fig. l; and

Fig. 3 is a somewhat diagrammatic illustration of pairs of involuteblades which have been generated from a generating circle of the samesize as that of Fig. 2, but with the center of the generating circle atdiiferent locations with respect to the center of the wheel.

The centrifugal fan wheel embodying the present invention has certaindesirable characteristics all of which contribute in a measure to theimproved result of being able to achieve a higher static suction and ahigher volume with a single wheel than has heretofore been accomplishedby the use of either single or multistage wheels. In designing the fanwheel disclosed herein there is illustrated the preferredcharacteristics although it will be understood that some of thesecharacteristics may be altered within limits without seriously affectingthe result.

For example, it was first determined by various tests that an involutewas the best form of blade which could be used to achieve the desiredresults. When it is considered that the involute of a circle is a curvegenerated by the end of a string which is kept taut while being unwoundfrom a circle, it will be understood that for a given diameter fan wheelit would be possible to utilize circles of various diameters. It is alsopossible to locate the center of the generating circle or evolute indifferent positions with respect to the center of the wheel and therebyobtain different results.

Consideration must also be given to the length of passage between theblades or to the length of the blades themselves because if the bladesare too long the resulting increased resistance to the passage of airtherethrough will adversely affect the results desired.

Furthermore, the angle of a tangent at the tip end of the blade with atangent to the wheel at the point where the tip end of the bladeterminates has a very definite cifect upon the results. For example, thegreater the angle the more feedback will occur resulting in less volumeand less static delivery. It follows that a smaller angle at the tip isdesirable although the smaller the angle the greater will be the lengthof the blade resulting again in increased resistance to air flow.

Consideration must also be given to the fact that the air which entersat the center of the fan wheel is relatively rareed and it is thereforedesirable that this air be compressed to a degree at the point of itsoutlet from the fan wheel. To achieve this result it was found desirableto have the inlet area between adjacent blades at the center of thewheel be greater than the outlet area between adjacent blades at theperiphery of the wheel.

The use of a true center involute where the center of the generatingcircle or evolute is common to the center of the wheel produces aplurality of blades which are parallel throughout their length resultingin inlet and outlet areas between adjacent blades which are identical;therefore, no compression of the fluid can take place. Also, when thisis done it has been found that the length of the blades createundesirable resistance thereby adversely affecting the result bydecreasing the volume.

ln order to arrive at a blade design of an involute form where the bladewas not too long, where the angle of a tangent at the tip end of theblade with the tangent on the periphery of the wheel at a pointcoincident with the blade tip would be small enough to reduce feedbackof the air, and where the inlet areas between adjacent blades Awould begreater than the outlet area thereof, it was necessary to conduct manyexperiments using generating circles of varying diameters and locatingthe centers of the generating circles at various distances from thecenter of the wheel. It was found that for a fan wheel having a sevenand one-half inch diameter the best results were obtained by usingblades of involute form where the involute was generated from a circleor evolute having a diameter of one and one-fourth inches. It was alsofound that for a fan wheel of six inch diameter, best results wereobtained by using a generating circle of one inch diameter to generatethe involute form of the blades. With this in mind the diameter of thegenerating circle should be about one-sixth of the diameter of the fanwheel to be used in order to achieve both the highest volume and higheststatic delivery.

ln arranging the involute blades which were generated from thepredetermined diameter of generating circle ground the wheel in such amanner to obtain minimum feedback, minimum resistance and desiredcompression of the uid, it become necessary to locate the center of thegenerating circle for each blade in offset relation with the center ofthe wheel. Various distances for the wheel center and various directionstherefrom were attempted with the result that the arrangement of theblade shown in Fig. 2 was determined to give maximum results.

Having the foregoing in mind, reference will now be made particularly tothe drawings and especially to Figi wherein it will be seen that the fanwheel is composed of the two axially spaced apart disks 1 and 2. Theupper disk 1 is commonly called the back of the wheel whereas the lowerdisk 2 is referred to as the shroud. The back 1 is provided with acentral opening 3 for the reception of a shaft and the shroud 2 has thecentral opening 4 therein to receive the compressible iluid such as airand direct it to the passages between the blades 5 as the wheel rotatesin a counterclockwise direction as viewed in Fig.

Each blade 5 is formed preferably of sheet metal and takes the form ofan involute curve. Fig. 2 represents the preferred embodiment of theinvention and illustrates the location of the involute blades to achievebest results. It will be understood that variation in the specificlocation of each involute blade 5 may be made without effectingsubstantially the end results but the greater the variation the greaterthe result will be affected. This will be brought out more clearlyhereinafter when specific reference is made to Fig. 3 which illustratesother locations of involute blades which are unsatisfactory.

The inner end 6 of each blade 5 is called the heel of the blade whereasthe outer end 7 is called the tip thereof. Having in mind that theresults with respect to both volume and static suction will varydepending upon the length of each blade, the inlet area between adjacentblades near the center of the wheel, the outlet area between adjacentblades at their tip ends, and the angle formed between the tangent tothe involute curve at the tip of each blade with the tangent to thecircle formed by the tips of the blades at the point where the tip ofthe blade meets such circle, all of these factors have been consideredin arriving at the particular layout of the blades shown in Fig. 2.

Experiments were conducted using disks 1 and 2 having a diameter ofseven and one-half inches. involute curves having various diameters ofgenerating circles were tried and it was determined that the bestresults were obtained with an involute curve having a generating circleof one and one-fourth inches in diameter. Other experiments with otherdisks of different diameters indicated best results to be obtained bythe use of involute curves having different diameters of generatingcircles. For example, when the disks 1 and 2 were six inches in diameterit was found that best results were obtained by the use of an involutecurve having a generating circle of one inch diameter. In this way itwas established that the preferred form of the invention should utilizean involute curve where the diameter of the generating circle issubstantially one-sixth the diameter of the wheel in which the bladesare to be used.

It will be noted in Fig. 2 that the blades 5 are laid Out in an involuteform where the involute is generated 'afferentefntafjeicekwisedireetien. viewingthesinne-wheelfeiern f the l oppositeside,==vth'e involutei bladeswold bei-generated in a counterclockwisedirection. Thisfctfniustbeborne ein nmnd Lwhen'defining-tl1eflocation fithe/ center Y of the Mgenerating #circle ffor u the -invlute -withrespect "to =the "fcenterlofr the same wheel.

When l"the :centerof the generating fcir'clle isv coincident l-Withl'*thecenter `f the wheely Aandi-'the invlutev 'blades-1 are fforined'inispaced apart relation, git'vvilll be evidentthat all fof vthereladesIwill-beparallel throughout their-#entire lengthinffaccordancewith1the`blades` 8 in Fig. 3. This arrangement 'does not Esatisfyitwofof the requirements mentioned above, namely, *that theinletfareafb'etween adjacent Ablades/be :greater thanfthe foutletiarea."'Where "the blades areparallel 1asfindica'ted by thefrlnmerallS thefilet-andoutletfareas vwill be substantially identical so "that 'nocompression `o`f1 theiiudewill''taketplace. VIt will salsoi 'betn'oted-` that; the "length of='bla'c`tes -`8::is AconsiderablyJgre'ater than the len'gthof'thefblades 'thereby/.resulting linincreasedvresistance'ito the' passage fof the :ui'd there- :between Itwas r thus 'discovered that fther fcenterr 'of the .generat-Ain'gvcirc'ile for the'invluteish'ouldvbe y'offset from thec'enter #ofthefan wheel'a'nd experimentation -was V'then -necessary to determinethie .'amount of the foffset and :the l-dlrection thereof fromthe-center fthe wheel. When :.-speakingtdf 'the centerfof the generatingcircle. being-offset tf1-om the .'centeno'f theifan wheelasfused herein,iitis understoodto"meanrthat v.the initial positionfof .the genlerating."circle 'is `:that vat which the :starting :point of :the involuteiis'at: the' left ofthe center ofthe ygenerat-ing circle and :inra.position tozg'enerate the involutein Ia clockwise tdirection.

:Fig 3fillustrates the results Iof'threexpositions of the :generatingcircle all of Vwhich produce Aunsatisfactoryresuits. 'The :positioningofthe *generatingcircle-so'tlrat --the center 'thereof Ais. coincidentwith the center'of the .fan -Ywheel ihas :already been vmentioned above.and was ,described asgresulting in the parallel'iblades f8. When,however, the center of the=generating circle y'is moved toward-thelefttof the center of the fan -wheel va distance equal -to theradius of 'the generating circle :so `that the `starting t points -ofall of-the :involute blades will be on :at circlexha-ving .a 'radiustwice that of the generating circle, -t-hes-result fwillbe toproduceblades like those indicated by :tlrenume'ral'9. It will, ofcourse,ebe'understood that for -each'blade :the generating circle is movedfrom-its initial starting, position-so that aflinegpa'ssing throughtherstarting tpointiof the vinvolute curve and the center "of thegenerat- :in-g circle willalso kpass through the center ofthe wheel..fThus the dot-.dash circle indicated `by lthe 'numeral -10 viszthatonwhich :each .involute begins.

When adjacent blades are separated a distance of 36degreesfso'thatitherewlllbea totltof ten L'biades for the wheel, it willbe :noted that thefblades9practically touch at one. point along theirlength so thatair passing from the inlet 11 lbetween adjacent 'bladestothe outlet '1'2will go through a compression stage and ythen anexpansion stage and the resistance thus offered for this reason and forthe additionalv reason `that the blades are unduly long willproduceivery'unsatisfactory results. The Volume will deini'tely'bedecreased due to :the increased resistance and thus the objective -ofmaintaining bothhigh volume and lhighs'tatic conditions-willnot-prevail.

When the position of the generating circle is initially as mentionedabove and then moved toward the right of the center of the fan wheel adistance equal to twice the .radius of the generating circle so that thestarting points of all involute blades will be on the circle identifiedby the numeral 13 the resulting blades will have the configuration ofthe blades indicated by the numeral 14. Again the blades 14 are spacedapart an angle of 36 degrees around a circle on any given radius fromthe center of the wheel to provide a total of ten blades only two ofwhich are shown in Fig. 3.

l'and the 'tangent tothe-periphery-of the wheel atthefpoint where theblade tip 'meets the periphery is 'relatively` large 'duci'n'g'iles'svolume. Y,

Further Vexperirnentation "indicated that positioning 'thegenerating-'circle of theinvolute Vtoward the `right of the center'of'thewhel when thefgenera'ting circle `is `positioned sof'thatthesta'r'tingfpcint er 'the "in'vclute is at the left of the center'ofythe'generatingcircle `and in afpositon to generate the .involute inaclockwise :direction produced improved results. -Thebestre'sultswerefound to obtain when the generating circlewas moved Etowa'i-ithe righta-distanc'e :equal to theradius-of thatcircle and that`isth'e lposition'of thef'blades 5 illustrated in Fig. `2. In this Vconlstructio'n thecenter of'thelge'nera'ting vcircle islocated 'at 'a point onthe c'irle Cso thatthe starting point of the involute for all blades is at thecenter'C-of the fan'wheel. All-"of lthefdesired conditionsare met inthisl construction.

For example;itlwillbenoted that the lengthl ofy blades li5 is 'less'thanthe'flengthof blades'Sor v9"in Fig. f2 thereby satisfyingone'requirementthat the blades ybe' 'of a length to createthe'rninirnurn resistancefor iuid'ilow when the lotherfa'ctors Aare alsoconsidered.

Also, since the axial distanceib'etween vthe two disks `1 fand2*"is'constar`1t'throughouttheir area thefdistance betweenblades 'at'their inletjandfoutletends will govern the inlet and outlet areas.y Theinlet :area 7between :adjacent blaies 5 maybe governed by thedistanc'ellrneasured on a perpendicularA lin'efro'rn the tangent atthe'heelof one blade'to the next adjacent blade. Likewise;theoutletarea:between adjacent bl'ades f is governed by the "distance `O 'betweenvrblades 'measured on a perp'endicular Iline lfrorn 'the tangent at'thetip 'cf one 'blade 'to its adjacent blade. 'Thus ic'will he seenthatfthedistanee ris greaterthanthe distance O so that the outlet "areais less `than'the inlet area and a compression" 'of the viiuidwillresult.

This arrangement also provides for a sinall'enough angle"between'thetangent at thetip of eaeh'blade andthe "tangent to thewheel'at the same point'so as to 'reduce leaklba'clc and thusinc'reasevolume.

Obviously, the center 'ofthe generating circle maybe initially movedtoward the right `of the center 'of the wheel under the conditionsabove'stated, varying distances to obtain'vaiying results. Ithis beenestablish'e'dfhowever, as is evident from viewing th'eblad'es 14 in Fig.3 that tnev'ing thecenter cf the'gen'erating circle teward'the right adistance 'twice the radius 4of the generating circle -will giveunsatisfactory v"results so that'it follows that'the 'distance towardthe right which this center should be moved must 'be 'a 'distance lessthan twice 'the radius of the generating circle.

`itha's also been'established that 'when the centers of 'the generatingcircle and of Ythe wheclare coincident the result is also unsatisfactorya's 'isjevident from viewing the blades '8 'on Fig. 3 since thebladesare'parallelthroughout their entire length and are relativelylong. Itithere'fore Afollows that for best results the center of thegenerating circle should be moved toward the right 'of the center A'ofthe wheel a distance less than twice the'r'adius of 'the generatingcircle and 'preferably a 'distance -equally substantially to the radiusof the generating circle as illustrated in Fig. 2.

Although the fan wheel embodying the present invention may be fabricatedin various ways, the preferred man` ner is to form each involute bladeof sheet metal with a plurality of ears along each edge of the blade inspaced apart relation. Each of the disks 1 and 2 embodying the back andthe shroud of the fan wheel is also provided with a series of slottedopenings, adapted to receive the ears on each of the blades. Each seriesof openings in a disk for each blade will be located along the line ofan involute of the same size as the involute used to produce the blades.The various parts are then assembled so that the ears 17 on each blademay extend through the corresponding slots on each disk. The ears 17 arethen bent over against each adjacent disk whereby all of the blades areheld in place in their proper relation positions.

Reference has heretofore been made to the static suction or closed waterlift obtainable by the use of a fan wheel embodying the presentinvention as illustrated in Figs. 1 and 2. In actual practice it hasbeen found that a fan wheel having a seven and one-half inch diameterwith ten involute blades spaced equally around the wheel having agenerating circle of one and one-fourth inch diameter and offsetaccording to the arrangement of Fig. 2 will produce a closed water liftof approximately sixtyseven inches. It has not been possible heretoforeto achieve that amount of closed water lift with a single stage fanhaving a diameter on the order of seven and one-half inches. The volumeobtainable in the present fan wheel is not reduced below that whichwould be obtained by any other single stage vacuum producing machine.Such other machines, however, in order to acquire a closed water lift ofsixty-seven inches would have to be provided with a plurality of fanwheels thus causing a considerable reduction in the volume obtainable.The present invention therefore results in unusually high static suctionand volume in the same machine with the use of but a single fan wheel.

It will be evident also that the number of blades used might vary withvarying results although it has been found that anywhere from eight totwelve blades will produce satisfactory results, the number of bladesbeing shown herein for purposes of illustration being ten.

Changes may be made in the form, construction and arrangement of partsfrom those disclosed herein without in any way departing from the spiritof the invention or sacrificing any of the attendant advantages thereof,provided, however, that such changes fall within the scope of the claimsapended hereto.

T he invention is hereby claimed as follows:

1. A centrifugal fan wheel comprising at least one disk, and a pluralityof blades of involute form disposed on said disk and secured thereto,the center of the generating circle for each involute blade being offsetfrom the center of rotation of the wheel.

2. A centrifugal fan wheel comprising two disks in axially spacedrelation, and a plurality of blades of involute form disposed betweensaid disks and secured thereto and arranged to be equal distances aparton any given radius from the center of the wheel, the center of thegenerating circle for each involute blade being offset substantially thesame distance from the center of ro tation of the wheel.

3. A centrifugal fan wheel comprising two disks in axially spacedrelation, and a plurality of blades of involute form disposed betweensaid disks and secured thereto, the center of the generating circle foreach involute blade being offset from the center of rotation of thewheel a distance less than the diameter of said generating circle.

4. A centrifugal fan wheel comprising two disks in axially spacedrelation, and a plurality of blades of involute form disposed betweensaid disks and secured thereto, the center of the generating circle foreach involute blade being offset from the center of rotation of thewheel a distance substantially equal to the radius of said generatingcircle.

5. A centrifugal fan wheel comprising two discs in axially spacedrelation, and a plurality of blades of involute form disposed betweensaid disks and secured thereto, the center of the generating circle foreach involute blade being offset toward the right from the center ofrotation of the wheel when the starting point of the involute curve isat the left side of the generating circle and the curve is generated ina clockwise direction, the amount of said offset being substantiallyequal to the radius of the generating circle.

6. A centrifugal fan wheel for compressible fluids comprising two disksin axially spaced relation, one of said disks having an inlet opening atthe center thereof for the passage of uid, and a plurality of blades ofinvolute form equally spaced around the wheel and between said disks,the center of the generating circle for each involute blade being offsetfrom the center of rotation of the wheel, and arranged so that the fluidinlet area between adjacent blades at the heels thereof is greater thanthe fluid outlet area between adjacent blades at the tips thereof,whereby the fluid will be compressed during the passage thereof betweenthe blades.

7. A centrifugal fan wheel for compressible uids comprising two llatdisks in axially spaced relation, one of said disks having an inletopening at the center thereof for the passage of fluid, and a pluralityof blades of involute form disposed between said disks and securedthereto and arranged to be equal distances apart on any given radiusfrom the center of the wheel, the center of the generating circle foreach involute blade being offset from the center of rotation of thewheel, and the distance on a perpendicular line from the tangent at theheel of any one blade to the next adjacent blade being greater than thedistance on a perpendicular line from the tangent at the tip of saidadjacent blade to the first blade, whereby the uid will be compressedduring the passage thereof between the blades.

8. A centrifugal fan wheel for compressible fluids comprising two flatdisks in axially spaced relation, one of said disks having a fluid inletopening at the center thereof, and a plurality of blades of involuteform disposed between said disks and secured thereto and arranged to beequal distances apart on any given radius from the center of the wheel,the center of the generating circle for each involute blade being offsetfrom the center of rotation of the wheel, and the area of the inletopening between adjacent blades being greater than the outlet openingbetween said blades, whereby fluid will be compressed during the passagethereof between the blades.

References Cited in the file of this patent UNITED STATES PATENTS2,165,808 Murphy July 11, 1939 FOREIGN PATENTS 23,234 Germany July 23,1883 115,070 Great Britain Apr. 22, 1918 121,052 Great Britain Dec. 5,1918 297,661 Great Britain Sept. 27, 1928 338,436 Germany Aug. 29, 1920

